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Worms and Mollusks

Ms. Moore 10/18/12. Worms and Mollusks. What is a flatworm?. Phylum: Platyhelminthes Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the simplest animals to have 3 embryonic germ layers , bilateral symmetry , and cephalization .

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Worms and Mollusks

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  1. Ms. Moore 10/18/12 Worms and Mollusks

  2. What is a flatworm? • Phylum: Platyhelminthes • Flatworms are soft, flattened worms that have tissues and internal organ systems. • They are the simplest animals to have 3 embryonic germ layers, bilateral symmetry, and cephalization. • Acoelomates: without coelom (fluid-filled body cavity, lined with tissue from mesoderm

  3. Flatworms: Form and Function • Feeding: • Carnivores or Scavengers ; can be parasitic • Digestive cavity with single opening (mouth) • Pharynx: extends outside the mouth and pumps food into digestive cavity (gut) • Food diffuses from the digestive cavity into all other body tissues

  4. Respiration, Circulation, and Excretion: • Since their bodies are so flat and thin, many flatworms do not need a circulatory system to transport materials (use diffusion). • No gills or respiratory organs; no heart, blood vessels, or blood. • Flame cells: specialized cells that remove excess water from the body; filter and remove ammonia and urea using pores of the skin

  5. Response: • Ganglia: groups of nerve cells that control the nervous system (no brain) • Eyespot: group of cells that can detect changes in the amount of light in their environment

  6. Movement: • Cilia on the epidermal cells help glide through the water. • Muscles controlled by the nervous system help to twist and turn to react to environment.

  7. Reproduction: • Hermaphrodite: both male and female reproductive organs • Sexual: two worms join in a pair and they deliver sperm to each other • Asexual: fissionorganism splits in two and each half grows new parts to become a complete organism

  8. Groups of Flatworms • Turbellarians • Flukes • Tapeworms

  9. Turbellarians • Free-living flatworms • Most live in marine or fresh water • Bottom dwellers: living in sand or mud • Planarians: “cross-eyed” freshwater worms

  10. Flukes • Class: Trematoda • Parasitic flatworms that infect internal organs of their host; can also be external parasites.

  11. Tapeworms • Class: Cestoda • Long, flat, parasitic worms that are adapted to life inside the intestines of their hosts. • Scolex: contains suckers or hooks; attaches • Proglottids: segments that make up most of worm’s body; contain male and female reproductive organs • Youngest proglottids are at the anterior end and the largest and most mature are at t he posterior. After eggs have been fertilized, proglottids break off and release zygotes that are passed out of the host in feces/ • Testes: fertilize eggs of other tapeworms or of self

  12. What is a Roundworm? • Phylum: Nematoda • Roundworms are slender, unsegmented worms with tapering ends; Range in size from microscopic to a meter in length • Pseudocoelom: false coelom (only partially lined with mesoderm • Digestive tract with two openings—mouth and anus (posterior opening of digestive tract) • “tube within a tube”: inner tube is digestive tract and outer tube is body wall • Food moves in one direction

  13. Roundworms: Form and Function • Feeding: • Carnivorous: eat small animals by latching on to them with grasping mouth parts and spikes • Scavengers: eat algae or decaying mater • Consume bacteria and fungi • The free living roundworms tend to be more complex than parasitic roundworms.

  14. Respiration, Circulation, and Excretion • Diffusion through body walls • Response • Simple nervous systems with several ganglia; sense organs that detect chemicals given off by prey or host • Movement • Muscles extend length of body; function as hydrostatic skeleton • Reproduction • Sexually with male and female worms • Internal fertilization

  15. Roundworms and Human Disease • Trichinosis-Causing Worms • Caused by Trichinella roundworm • Worms burrow into intestine walls and females release larvae that travel through the bloodstream and live in organs and tissues of host’s body

  16. Filarial Worms • Found in tropic regions of Asia; live in blood and lymph vessels of birds and mammals (humans) • Transmitted host-to-host by biting insects like mosquitoes • Large numbers could block lymph passageselephantiasis

  17. Ascarid Worms • The cause of malnutrition of more than 1 billion people worldwide. • Ascarislumbricoidesusually spread by eating vegetables that are not washed properly.

  18. Hookworms • 25% of the world’s population is infected with these worms • Eggs hatch outside the body and mature in the soil • Use tooth-like plates to burrow into skin of an uncovered foot and live in bloodstream • Suck blood and cause weakness and poor growth

  19. Research on C. elegans • DNA sequence has been mapped out (97 million bp) • Help us find out how eukaryotes become multicellular and how multicellular animals are similar and different

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